﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace Cat.Utility
{
    public static class OrderExpression
    {
        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "OrderBy");
        }
        public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "OrderByDescending");
        }
        public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "ThenBy");
        }
        public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
        {
            return ApplyOrder<T>(source, property, "ThenByDescending");
        }
        static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
        {
            string[] props = property.Split('.');
            Type type = typeof(T);
            ParameterExpression arg = Expression.Parameter(type, "x");
            Expression expr = arg;
            foreach (string prop in props)
            {
                PropertyInfo pi = null;
                // use reflection (not ComponentModel) to mirror LINQ  
                try
                {
                    pi = type.GetProperty(prop);
                }
                catch (Exception ex)
                {
                    if (ex.Message == "Ambiguous match found.")
                        throw new Exception("发现不明确的匹配，请检查指定的排序字段是否属于实体");
                }
                //if (pi == null)
                //    throw new Exception("没有找到指定名称的公共属性");
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }
            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);

            object result = typeof(Queryable).GetMethods().Single(
                    method => method.Name == methodName
                            && method.IsGenericMethodDefinition
                            && method.GetGenericArguments().Length == 2
                            && method.GetParameters().Length == 2)
                    .MakeGenericMethod(typeof(T), type)
                    .Invoke(null, new object[] { source, lambda });
            return (IOrderedQueryable<T>)result;
        }

        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property, string sortOrder)
        {
            if (sortOrder.ToLower() == "asc")
                return ApplyOrder<T>(source, property, "OrderBy");
            else
                return ApplyOrder<T>(source, property, "OrderByDescending");
        }
        public static IOrderedQueryable<T> ThenBy<T>(this IQueryable<T> source, string property, string sortOrder)
        {
            if (sortOrder.ToLower() == "asc")
                return ApplyOrder<T>(source, property, "ThenBy");
            else
                return ApplyOrder<T>(source, property, "ThenByDescending");
        }
        public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, Dictionary<string, string> dicOrderBy)
        {
            if (dicOrderBy != null)
            {
                var isFirst = true;
                foreach (var orderBy in dicOrderBy)
                {
                    if (isFirst)
                    {
                        source = source.OrderBy(orderBy.Key, orderBy.Value);
                        isFirst = false;
                    }
                    else
                        source = source.ThenBy(orderBy.Key, orderBy.Value);
                }
            }
            return source;
        }
    }

}